class Solution {
    int dx[4] = {0, 0, -1, 1};
    int dy[4] = {1, -1, 0, 0};

public:
    int numEnclaves(vector<vector<int>>& grid) {
        int m = grid.size(), n = grid[0].size();
        queue<pair<int, int>> q;
        for(int j = 0; j < n; ++j) // 1. 处理边界的1
        {
            if(grid[0][j] == 1) // 第一行
            {
                grid[0][j] = -1;
                q.push({0, j});
            }
            if(grid[m - 1][j] == 1) // 最后一行
            {
                grid[m - 1][j] = -1;
                q.push({m - 1, j});
            }
        }
        for(int i = 0; i < m; ++i)
        {
            if(grid[i][0] == 1) // 第一列
            {
                grid[i][0] = -1;
                q.push({i, 0});
            }
            if(grid[i][n - 1] == 1) // 最后一列
            {
                grid[i][n - 1] = -1;
                q.push({i, n - 1});
            }
        }

        while(!q.empty())
        {
            auto[a, b] = q.front();
            q.pop();
            for(int i = 0; i < 4; ++i)
            {
                int x = a + dx[i], y = b + dy[i];
                if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 1)
                {
                    grid[x][y] = -1;
                    q.push({x, y});
                }
            }
        }

        int ret = 0;
        for(int i = 0; i < m; ++i)
        {
            for(int j = 0; j < n; ++j)
            {
                if(grid[i][j] == 1)
                    ++ret;
            }
        }
        return ret;
    }
};